1. Field of the Invention
This invention relates to curable liquid organosiloxane compositions. More particularly, this invention relates to emulsions wherein the continuous phase comprises at least one carboxyalkyl terminated polydimethylsiloxane and the dispersed phase comprises at least one epoxide compound selected from diglycidyl ethers of di- and bis-phenols. The emulsions also include a curing catalyst in addition to a dispersing agent for the epoxide compound, and can be cured with heating to form elastomeric materials.
2. Background Information
The copolymerization of organic compounds containing two or more epoxide groups with organosilicon compounds having a plurality of epoxide-reactive groups has been disclosed as a means for preparing materials ranging from resins to elastomers.
The reaction of epoxide compounds with organosilicon compounds containing at least one hydroxyl group per molecule under anhydrous conditions and in the presence of an aluminum-containing catalyst is described in U.S. Pat. No. 3,971,747, which issued to Banks et al. on July 27, 1976.
The reaction of epoxide compounds with organosiloxanes containing various epoxide-reactive functional groups to yield resinous products is disclosed in U.S. Pat. No. 2,819,245, which issued to Shorr on Jan. 7, 1958, and in U.S. Pat. No. 2,846,560, which issued to Mika on July 15, 1958.
Coating compositions containing from 35 to 85 percent by weight of an epoxide compound, such as diglycidyl ethers of difunctional alcohols or cycloaliphatic epoxide compounds, from 15 to 65 percent by weight of a specified group of hydroxyl-containing polyorganosiloxanes and a catalytically effective amount of a chelated aluminum compound are disclosed in U.S. Pat. No. 4,332,923 that issued to Rainear on June 1, 1982. This patent also teaches that if the desired epoxide compound(s) and polyorganosiloxane(s) are immiscible, the composition can be in the form of an oil-in-oil emulsion that includes a surfactant of the type described in U.S. Pat. No. 3,926,885, which issued to Keil on Dec. 16, 1975. The Keil patent concerns self-lubricating epoxide compositions wherein the lubricant is incompatible with the epoxide compound and is present as a dispersed phase in a matrix of the epoxide compound. The dispersed phase is stabilized using specified classes of dispersing agents. Liquid polydimethylsiloxanes constitute a preferred class of lubricants.
One type of dispersing agent disclosed in the Keil patent is a polydimethylsiloxane-organic copolymer wherein the polydimethylsiloxane portion has a molecular weight of at least 1500 and preferably constitutes from 9 to 91 percent by weight of the dispersing agent. The organic portion consists essentially of polyoxyethylene units, polyoxypropylene units, or a combination of these two units.
In accordance with the present invention, it has been found that polydimethylsiloxane-organic copolymers containing repeating units of the types described in the aforementioned Keil patent, but wherein the concentration of organic units is above the disclosed limit of 91 weight percent, are one of two classes of dispersing agents that will stabilize oil-in-oil emulsions wherein the dispersed phase is an epoxide compound and the continuous phase is a liquid carboxy functional polydiorganosiloxane containing at least 95 mole percent of dimethylsiloxane units. Because the polyorganosiloxane rather than the epoxide is the continuous phase, the properties of the cured compositions are characteristic of silicone rubber rather than the resinous epoxide products obtained by following the teaching of the Keil patent. Unlike moisture-curable polyorganosiloxane compositions, the compositions of this invention can be completely cured in any thickness.